Method for making electrical terminals



March 12, 1957 T. w. GRIFFITHS METHOD FOR MAKING ELECTRICAL TERMINALSOriginal Filed June 21, 1946 was 35' In ve ntor TWGRI FFITHS m A homeyMETHOD FGR MAKING ELECTRICAL TERMMALS Thomas William Grilhths, Newark,N. 3., assignor to International Telephone and Telegraph Corporation, acorporation of Maryland Original application June 21, 1946, Serial No.678,173. Digided and this application March 5, 1952, Serial No. 27 ,727

ll Claim. (Cl. 49 m) This is a divisional application of my parentapplication Serial No. 678,173, filed June 21, 1946, now ab'andoned.

This invention relates to electrical terminal devices and moreparticularly to electrical terminals of the type which arecarriedthrough glass seeds.

The principal object of the invention is to provide a method for makinga terminal of this type which provides a high degree of insulation andrelatively great strength of the sealing means.

It has been a practice to carry an electrical terminal rod through aglass seal, such as a glass bead which is sealed through an aperture ina suitable supporting device such as a metal base or cap or the like.Difficulty has sometimes been encountered, however, in carrying out thispractice. An important difliculty has been the lack of strength of theconstruction. For example, a blow on the protruding end of the terminalhas sometimes resulted in shattering of theglass bead and consequentdisruption of the terminal. Another disadvantage has been that theshortness of the path along the surface of the bead from the terminal tothe supporting base has sometimes permitted a substantial amount ofelectrical leakage along the surface of the glass forming the seal.

One expedient which has heretofore been proposed in an attempt toprovide a greater surface and strength of the seal has been to soften ormelt a rather thick rod of glass above a metallic aperture through whichthe terminal is to be sealed, and allow the glass to droop down throughthe aperture to form a bead below it. Although such a seal hasconsiderable merit, it has the disadvantage that the bead formed by theglass drooping below the aperture has not had as great a surface as isdesirable, and furthermore has not provided as much strength as isdesirable.

By means of my present invention, 1 overcome the foregoing disadvantagesby a construction providing great strength coupled with a long pathalong the glass between the terminal and the supporting base member.Furthermore, I provide a strong, resilient construction which tends toavoid shattering of the parts and resists mechanical shock.

I carry out my invention by the provision of an elongated shape of thesealing glass, such that theglass extends for a relatively greatdistance along the terminal member and provides a considerable extent ofglass from the extremity of the sealing of the glass to the terminal andto the base. To facilitate the sealing, the metallic base member ispreferably of a curved annular construction.

According to a feature of my invention, I insert a terminal rod ormember through a central hole passing through a glass rod which isinserted through the aperture of the base member or cap by which theseal is to be held; and I provide means for supporting the metallicaperture and providing space for the glass rod to flow rate Patent intowhen it is'heated and softened. Then, by softening the glass in an oven,it flowsinto the desired shape.

Accordingto aspecific variation of the foregoing feature, I use a moldshaped according to the desired shape of at least part ofthe glass seal,so that when the glass is melted it flows enough to fill the mold andprovide the desired shape. A feature is that the softening causes adesired flowing and rounding of the surfaces of the glass, causing it toadhere in a desired manner to the aperture and to the terminal.

The foregoing and other features of my invention will be betterunderstood from the following detailed description and the accompanyingdrawings of which:

Fig. l is an elevation view in cross section, taken'at line 1-1 of Fig.2, of a sealedterminal constructedaccording to my invention;

Fig. 2 is a crosssection view, taken at line 2-2 of Fig. 1;

Fig. 3 is an elevation view in cross section, taken at line 3-3 ofFig.4, showing a modified form of scaled terminal according tomyinvention;

Fig. 4 is a cross section view, taken at line 4-4 0 Fig.3;

Fig. 5 shows apparatus and a method of forming a seal, constructedaccording toFigs. l and 2;

Fig. 6 is an elevation view of a glass rod used in making the sealaccording to Fig. 5;

Fig. 7 is atop view of the glass rod shown in Fig. 6; and

Fig. 8 shows apparatusand a method of molding a glass seal to providethe construction shown in Figs- 3 and 4.

In the sealed terminal arrangement of Figs. land 2, there is shown aterminal rod 1 of a suitable metal such as Kovar, passing through anaperture formed through a metallic supporting member 2, which may alsobe of a convenient sealing material such as Kovar. The apertured memberis in the form of a flatplate 3, having an annular depending collarportion 4 curved to form :an inwardly protruding flange member-5; andending in a lower circular lip 6. The sealing glass 7 isin the form ofan elongated seal extending through a substantial length of the rod 1,beginning at an upper point 8 above the aperture and falling downwardlyand outwardly, forming a surface of revolution in a concave curved shape9 to the upper end of the aperture plate. The lower part of thesealing'glass is in the form of an elongated convex surface ofrevolution 11 starting at the outer edge 12 of the lower lip 6 of theaperture, and extending downwardly in the form of an elongated convexbead to a point 13 on the rod 1 well below the aperture. The distance din the axial direction of the rod is substantially greater than themaximum radius r of the lower bead, thereby providing a path ofconsiderable length from lip 6 to point 13. The length of the path alongconcave surface 9 from point it) to point 8 is preferably about the sameas the length of path from point 6 to point 13. This provides longelectrical leakage paths from the support 2 to the terminal rod.

The composition of the glass should be one which really seals to theterminal rod and to the base support. Suitable glass compositions forthis purpose, including those especially suited for sealing to Kovarmetal are' well known, and need no further discussion here.

In Figs. 3 and 4, which showanother modification of a sealed terminalconstructed according to my invention, the terminal rod 1 is carriedthrough an aperture which is shaped somewhat different from that inFigs. 1 and 2. In Fig. 3, the aperture is extruded through the flatplate 3 so as to provide'a raised curved bead 14 having adepending lip15. The glass seal member 16 1s shaped somewhat difierent from the glassmember 1n F g. 1, since the upper part is in the shape of substantlallya cylinder 17, which is tapered upwardly slightly conlcally from a point18 at substantially the top of the bead 14, to a region 19 which isalmost flat, although extendmg upwardly slightly conically to a point 20which Is the uppermost point of scaling to the rod 1.

The lower portion 21 of the sealing glass is in the elongated convexbead-like shape, substantially like the lower portion of the seal inFig. 1. As in Fig. 1, the lower section 21 extends to the outer surfaceof the lower lip 1 5 of the aperture, being sealed to the outer edge 22.

Flg. 5 shows an arrangement by which the form of seal shown in Figs. 1and 2 may be made. There is used a block 23 of a refractory material,such as carbon, and the block is provided with a cylindrical bore oropening 24, large enough in diameter to accommodate the flange 4 of theaperture plate, while allowing the top portion 3 to rest on the top ofthe block, the flange 4 fitting nicely within the hole 24. The lower endof the hole 24 is carried inwardly and downwardly on a tapered surface25 to a central hole 46, large enough In diameter to receive theterminal rod 1.

The glass sealing substance is provided by a solid cylinder 26 of thesealing glass as shown in Fig. 6, the glass cylinder being of the properdiameter to fit nicely through the lip 6 of the aperture, and beingprovided with a central hole 27 of the proper diameter to receive therod 1.

The rod 1 is inserted through the hole 27 and into the bore or hole 46of the refractory block; and the glass cylinder 26 is fitted through thelower lip 6 of the aperture member, the device is held securely by theblock arrangement. In this condition, the block containing the terminalrod and glass cylinder is placed on a platform 28 in an oven, which isbrought to a sufficiently high temperature to soften the glass.

The temperature to which the oven is raised will depend in large measureupon the composition of the glass. It is desired that the heating shallbe just suflicient to soften the glass, causing it to sag and flowsomewhat, but not sufficient to melt the glass and allow it to flowfreely into all the cavities and places within the block. By carefullycontrolling the temperature of the oven in this way, and usingsuflicient time, the softening of the glass is accompanied by a changein shape from the cylindrical form of the glass rod to the form shown bythe dotted lines 30 and 31 in Fig. 5. Thus, the upper portion of thecylindrical glass rod will seal to the terminal rod at the upperextremity of the glass, as soon as the temperature is raised highenough, and the outer edges will then sag somewhat, sufiicient to fillthe annular space 29 between the cylindrical rod and the flange 4 of theaperture. When the glass flows down into this space, it seals to themetal of the aperture.

At the same time, the glass below the aperture tends to flow outsomewhat to the outer edge 12 of the lower lip of the aperture, therebyrounding out according to the dotted line 31 in Fig. 5. In this way, theseal takes the form shown in Fig. 1.

The seal shown in Figs. 3 and 4 maybe made in a somewhat similar mannerto that in Figs. 1 and 2, al-

though this form is a molded form rather than a flowed form of seal. Thetemperatures used will be higher than in the case of Fig. 5, and theglass will actually be melted and caused to flow. For this purpose thereis provided a lower carbon block 32 and an upper block 33. The lowerblock is provided with a well 34 with tapering sides as shown, andterminating in the almost flat conical taper 35, the lower end of thiswell terminating in a hole 36 large enough to receive the terminal rod1.

The block is suitably rounded so that it snugly fits the flange 14 ofthe aperture member when it is laid on the top of the block in aninverted position. The upper block 33 is provided with a cylindricalopening i or hole 37 of such a diameter that it fits snugly against theouter surface of the depending lip 15, and is fitted closely over theplate 3.

Before the terminal rod 1 is passed through the glass cylindrical member26, the upper part of it is first coated with a coating material 38 downto a point 39, this coating material being of a nature well known in theart which will prevent the glass from scaling to it when the glass ismelted. When the carbon blocks containing the structure are placed onthe platform 28 in the oven, and the oven temperature turned up abovethe melting point of glass, the glass will flow, filling the space 34between the cylindrical glass rod and the wall of the well in carbonblock 32. The glass required to fill this space will come from the upperportion of the cylindrical glass rod above the aperture; andaccordingly, the glass will tend to drop down into the lower well tofill the space. In dropping down, it will not seal to the coated portion38 of the terminal rod, but will only start to seal at the uppermostportion 39 which is at the lower end of the coating. Since the sealingstarts at this point, the glass will then tend to drop down and form theconvex surface 40 represented by the dotted lines in Fig. 8; and theglass will extend downwardly and outwardly to the outer edge of the lip15, as shown. When the glass has reached this position, the heat may beturned ofi, and it may be allowed to solidify, thereby remaining in'theshape shown by the dotted line 40 and by the shape of wall 34 of thewell. This is the shape shown in Fig. 3.

In the arrangement of Fig. 8, the upper curved block tends to shield theupper part of the seal from the heated platform 28 so that it does notmelt and run to as great a degree as at the lower part of the seal. Inconsequence, the upper part tends to hold its position better and forminto the curved rounded shape which is shown, while the lower part ismore thoroughly melted to run and fill the lower cavity.

After the glass has been molded and formed into the shape of Fig. 3 bythis procedure, it should preferably be annealed while in the mold bycontinuing to heat it at a temperature somewhat below the melting pointfor a period of time, after which it may be cooled and then removed fromthe mold. The somewhat tapered shape of the portion 16 will facilitatethe removal from the mold.

The best temperatures to use for causing the glass to flow will dependsomewhat on the size of the glass used, which in turn will depend on thesize of the aperture through which it is to be set. Not only will thebest tem perature depend upon the size of the glass piece, but as notedbefore, will also depend on the type or composition of the glass, sincethe melting points of different compositions will be different.Moreover, the best operating temperature will also be determined in somedegree by the annealing characteristics of the glass, and atmosphericconditions and the particular ultimate shape and propertions which it isdesired to impart to the surfaces.

In both the arrangements of Figs. 5 and 8, the terminal rod 1, restingdirectly on the hot platform 28, gets hotter than thecarbon blocks sothat the rod is the hottest part. This tends to cause the glass to sealreadily to the rod at the extremities shown, which facilitates theforming and warping of the glass into its desired configuration.

It will be recognized that by my invention, I have pro- 0 vided anespecially satisfactory form of seal for a terminal member and a methodof forming it. The seal is both tough and durable, and has the markedadvantage of providing large electrical leakage paths which provides thedesired high resistance between the terminal and the supporting base.The form of seal moreover, is resilient; and even though cracks shouldtend to form in the glass, they generally tend to form only around theedges or flanges where they do not materially damage the effectivenessof the seal. For example, in Fig. 1, such cracks as may tend to formwill most likely occur around the upper periphery at position 41, justinside the flange 4.

The particular combinations of the seal and aperture of Fig. 3 isespecially advantageous because the rib 18 provides a very high degreeof resilience. In the event of a tendency to bend the rod 1 or knock itsideways, the aperture plate will tend to give at position 42 therebyminimizing the likelihood of breakage of the seal.

Although only two forms of seal according to my invention areillustrated herein, it will be recognized that the invention is notlimited to these forms, but only in accordance with the appended claim.

Furthermore, it will be recognized that the form of terminal and seal isapplicable to a multiple terminal arrangement. For example, it issometimes desirable to have a plurality of terminals pass through thecover of a hermetically sealed casing. The practice of my invention maybe used for this purpose by providing the cover plate with the desirednumber of apertures of the type described herein and providing aterminal and seal through each aperture. The heating arrangements inFigs. 5 and 8 may be readily modified to provide the desired number ofaccommodations or holes for the number of apertures of the plate.

I claim:

The process of sealing an electrical conductor to a base member bymounting the conductor in a tubular glass member and positioning theglass member and conductor snugly in an aperture in the base member,whereby the base member is located intermediate the ends of the tubularglass member, and mounting the tubular member and conductor within aheating mold which completely surrounds said glass member and conductor,which process comprises applying heat to said mold in sufiicient degreeto cause the glass member on both sides of said base member to becomesufiicien-tly fluid to make sealing contact therewith and with saidconductor, to cause the glass on one side of said base member to becomefluid only to the extent that the diameter thereof is. maximum at thebase member and gradually decreases at is extends away therefrom, and tomelt the glass on the other side of said base member, to fill thesurrounding cavity of the mold.

References Cited in the file of this patent UNITED STATES PATENTS230,709 Lomax Aug. 3, 1880 732,812 Anderson July 7, 1903 1,562,533Weintraub Nov. 24, 1925 2,071,597 Vasselli Feb. 23, 1937 2,125,315 RonciAug. 2, 1938 2,174,374 Beggs Sept. 26, 1939 2,299,750 Hull et al. Oct.27, 1942 2,318,435 Stopakoff et al. May 4, 1943 2,338,538 Pulfrich eta1. Jan. 4, 1944 2,496,303 Morse et al. Feb. 7, 1950

